Conventionally, in cell site design, in most cases, indoor/outdoor communication-environment measured values collected by radio-wave measuring vehicles, area testers, and experiment stations, and simulation results (estimated values) of radio-wave propagation characteristic simulated by a computer are both used, and kinds of base stations, installation site candidates, and the like are determined (Non-patent Document 1). In the computer simulation, in general, wireless communication characteristic such as radio wave passages or propagation loss is calculated based on geographical information of topography, buildings, and the like and based on specific data of a base station.
In the simulation, in order to improve analysis accuracy, a plurality of analysis methods are sometimes used depending on regional characteristics of calculation-target areas. For example, the following Patent Document 1 discloses that Sakagami model is used for urban areas and Okumura-Hata model is used for suburban areas (paragraph [0029]). Further, Non-patent Documents 2discloses that an optimum model is selected from aplurality of radio-wave-propagation estimation models such as ray trace (ray launching method), Okumura-Hata model, Sakagami model, and free-space model for each of a plurality of radio-wave propagation environments such as urban areas, suburban areas, and indoor areas, and that radio-wave propagation simulation is executed.
That is, according to statistical analysis methods such as Okumura-Hata model and free-space model, it is possible to execute simulation with a high degree of accuracy and at high speed for a suburban area in which there are a small number of shield objects and vision area of a base station is wide, but desired accuracy cannot be obtained for an urban area in which there are many buildings or objects which affect radio wave propagation, which is problematic. Because of this, it is effective to analyze an urban area based on a quasi-experience model such as Sakagami model or based on a deterministic analysis method such as ray tracing method (ray launching method or imaging method).
Further, Patent Document 2 discloses an invention capable of reducing a calculation-process amount in a case of estimating radio-wave receiving characteristic in a service area based on imaging method. According to this invention, constructions (buildings and the like) in the vision of a sending point (base station) and constructions in the vision of a receiving point (mobile station) are only considered, whereby a target of tracing a passage of a radio wave (ray) from a sending point to a receiving point is minimized, and calculation process may be performed at an extremely high speed (claim 1, paragraph [0022], and the like).
Further, Patent Document 3 discloses an invention in which, in a case of calculating a visibility rate in an area covered by a base station, a visible side surface of a visible building in the area is recognized, and a visibility determination point is set on a straight line that forms the side surface. As a result, according to this invention, a calculation amount is greatly reduced compared to a case where a plurality of grid points on a roof surface of a building and a building center point are set as determination points. Further, in accordance with a mode in which a wireless-station antenna is installed on a balcony, a building wall surface, or the like, this invention is capable of executing determination more realistically and with a higher degree of accuracy.
Non-patent Document 1: “Computer Aided Practical Cell Design System” NTT DoCoMo Technical Journal Vol. 4, No. 1, pp. 28-31, 1996-04
Non-patent Document 2:  http://www.kke.co.jp/news/2008/pdf/NewsRelease_wireless.pdf
Patent Document 1: Japanese Patent Application Laid-open No. 2004-304302 (paragraph [0029])
Patent Document 2: Japanese Patent Application Laid-open No. 2005-72667 (claim 1, paragraph [0022])
Patent Document 3: Japanese Patent Application Laid-open No. 2006-352551 (claim 1, paragraph [0018])